Synthesis, Molecular Structure and Properties of the [H_6−nNi₃₀C₄(CO)₃₄(CdCl)₂]ⁿ⁻ (n=3–6) Bimetallic Carbide Carbonyl Cluster: A Model for the Growth of Noncompact Interstitial Metal Carbides

Abstract

Reaction of the [Ni(9)C(CO)(17)](2-) dianion with CdCl(2)2.5 H(2)O in THF affords the novel bimetallic Ni--Cd carbide carbonyl clusters [H(6-n)Ni(30)C(4)(CO)(34)(micro(5)-CdCl)(2)](n-) (n=3-6), which undergo several protonation-deprotonation equilibria in solution depending on the basicity of the solvent or upon addition of acids or bases. Although the occurrence in solution of these equilibria complicates the pertinent electrochemical studies on their electron-transfer activity, they clearly indicate that the clusters [H(6-n)Ni(30)C(4)(CO)(34)(micro(5)-CdCl)(2)](n-) (n=3-6), as well as the structurally related [H(6-n)Ni(34)C(4)(CO)(38)](n-) (n=4-6), undergo reversible or partially reversible redox processes and provide circumstantial and unambiguous evidence for the presence of hydrides for n=3, 4 and 5. Three of the [H(6-n)Ni(30)C(4)(CO)(34)(micro(5)-CdCl)(2)](n-) anions (n=4-6) have been structurally characterized in their [NMe(3)(CH(2)Ph)](4)[H(2)Ni(30)C(4)(CO)(34)(CdCl)(2)]2 COMe(2), [NEt(4)](5)[HNi(30)C(4)(CO)(34)(CdCl)(2)]2 MeCN and [NMe(4)](6)[Ni(30)C(4)(CO)(34)(CdCl)(2)]6 MeCN salts, respectively. All three anions display almost identical geometries and bonding parameters, probably because charge effects are minimized by delocalization over such a large metal carbonyl anion. Moreover, the Ni(30)C(4) core in these Ni-Cd carbide clusters is identical within experimental error to those present in the [HNi(34)C(4)(CO)(38)](5-) and [Ni(35)C(4)(CO)(39)](6-) species, suggesting that the stepwise assembly of their nickel carbide cores may represent a general pathway of growth of nickel polycarbide clusters. The fact that the [H(6-n)Ni(30)C(4)(CO)(34)(micro(5)-CdCl)(2)](n-)(n=4-6) anions display two valence electrons more than the structurally related [H(6-n)Ni(34)C(4)(CO)(38)](n-) (n=4-6) species has been rationalized by extended Hückel molecular orbital (EHMO) analysis.

Synthesis, Structures and Electrochemistry of New Carbonylnickel Octacarbide Clusters: The Distorting Action of Carbide Atoms in the Growth of Ni Cages and the First Example of the Inclusion of a Carbon Atom within a (Distorted) Ni Octahedral Cage

“…Crystals n-(n = 2-4; X = Cl, Br), [14] [H 6-n Ni 30 C 4 (CO) 34 (CdX) 2 ] n-(n = 3-6; X = Cl, Br, I) [12] and [H 7-n Ni 32 C 4 (CO) 36 (CdX)] n-(n = 5-7; X = Cl, Br, I). [13] Only n-(n = 6, 7; y = 0, 1; see the next section).…”

“…As illustrated in Figure 6a Because the very small current intensities due to both the very low diffusion coefficient of the high-nuclearity cluster and its limited solubility prevented any experimental measurement of the number of electrons involved in the different redox processes, we confidently assigned them to one-electron processes. [12] www.eurjic.org Figure 6c also shows that two more cathodic processes (asterisked peak systems) are present, which are attributed to by-products arising from the chemical complications accompanying the second main reduction. In fact, analysis of the cyclic voltammograms with scan rates progressively increasing from 0.02 to 0.5 V s -1 indicates that the oxidation and the first reduction processes are chemically and electrochemically reversible, whereas the second reduction is accompanied by chemical complications (as suggested by the value of the i pa /i pc ratio, which increases from 0.5 at 0.05 V s -1 to 1 at 0.2 V s -1 ).…”

“…[12] Electrochemical studies in CH 3 n-(n = 2-4; Table 3). As illustrated in Figure 6a Because the very small current intensities due to both the very low diffusion coefficient of the high-nuclearity cluster and its limited solubility prevented any experimental measurement of the number of electrons involved in the different redox processes, we confidently assigned them to one-electron processes.…”

“…These species are polyhydrides that display protonation-deprotonation equilibria depending on the basicity of the solvent, as previously found for other high-nuclearity MCCs. [12][13][14][15] In particular, the species directly obtained by performing the reaction in thf is the dihydride trianion [H 2 n-(n = 3-6) [12] are formed. Conversely, by operating in acetone with a large excess of CdCl 2 ·2.5H 2 n-(n = 2-4) [14] is obtained.…”

Topological insights in polynuclear Ni/Na coordination clusters derived from a schiff base ligand

“…Clusters of this size incorporate simple modified ligands with a wide variety of coordination modes for bridging, such as diethanolamine [42], Schiff base [43], carbide [44,45] and carboxylate [46]. The introduction of bridging groups can increase the nuclearity of a CC.…”